Amplifier tube having a thermionic cathode without heater



Nov. 10, 1964 AMPLIFIER TUBE w. VEITH 3,156,844

HAVING A THERMIONIC CATHODE WITHOUT HEATER Filed Aug. 31, 1960 UnitedStates Patent 3,156,844 AMTPLIFIER HAVING A THERh lifihllfi QATHDEWETHGUT iii LATER Werner Veith, Munich, Germmy, assignor to SiemensHalshe Alrtiengeseiischatt Berlin and Munich, a corporation of GermanyFiled Aug. 31, 1960, Ser. No. 53,l35 Claims priority, applicationGermany Sept. 1'8, 1959 9 Claims. (Cl. 313-305) This invention isconcerned with a high vacuum amplifier tube having a thermionic cathode(oxide cathode) without heater.

Amplifier tubes with thermionic cathodes have as compared withtransistors among others the considerable drawback that they requireadditional heating and therefore the presence of an appropriate heatingvoltage.

The present invention is based upon the following thoughts: In thecourse of investigations, involving above all the operation of amplifiertubes with thermionic cathodes, there is observed as a disturbingphenomenon the known intermediate layer resistance which appears as aresult of the formation of a poorly conducting layer between themetallic support and the emitting oxide mass proper. Such intermediatelayer resistance appears in the form of a feedback which is disturbinglynoticed particularly in the case of low frequencies and also reduces thelife of the tubes since it often constitutes a barrier for thepenetration of activators from the nickel support, which are requiredfor the activation. The electron stream emitted from the surface must inany case pass this intermediate layer and produces at the surface avoltage drop and therewith Ioules heat. It is possible to obtainintermediate layers which are so far as the resistance value isconcerned so considerable that the heat produced therein by the emissioncurrent suflices for maintaining the cathode at a temperature requiredfor the emission even without applying the customary heating by the useof a heater. A stable equilibrium will thereby occur since theintermediate resistance will always increase upon decrease of thetemperature, thereby causing again generation of more heat. A firingoperation is however required in the case of an amplifier tube equippedwith such a cathode, to produce with an initially low emission currentflowing over the intermediate resistance layer an initial heat whichsutfices for the initiation of the thermal emission.

The object of the invention is to produce a high vacuum amplifier tubewith thermionic cathode without the use of the customary heater, whichis characterized by simple electrode construction and operates reliablythroughout a normal useful life.

This object is realized by the provision, in connection with anamplifier tube of the initially described kind, of a cathode with anartificially produced intermediate layer resistance which is pronouncedas compared with a normal oxide cathode, and in which is responsive topassage therethrough of the emission current which is constant duringthe operation, substantially generated the heat required for the cathodetemperature, and by the provision of at least one auxiliary electrode(auxiliary anode) forming with the cathode an auxiliary discharge pathfor effecting the initial emission. An artificial intermediate layerresistance is for this purpose produced by the provision of aninsulating layer between the metallic cathode carrier and the customaryemission mass. Substances suitable for this purpose are, for example,aluminum oxide, magnesium oxide or calcium oxide, that is, oxides of theearth alkalior related earth metals. The emission layer is formed byusing oxides of earth alkali metals such as barium, strontium andcalcium, customarily employed for oxide cathodes, or, in the case of lowcurrent,

3,156,844 Patented Nov. 10, 1964 magnesium oxide, which are developedWithin the discharge vessel from the corresponding carbonates during theforming operation.

The initial emission for the so-called firing operation may be producedby light-electrical eiiect or by secondary emission at the emissionlayer proper. A further advantageous possibility for the passage ofelectrons through the intermediate layer resistance, for achieving theinitial heating, resides, according to the invention, in covering thesurface of the oxide cathode with several metallic rods and directlyconnecting thereto, for example, in common, over a very high ohmicresistor the anode voltage or a corresponding positive potential.

The foregoing and further objects and features of the invention willappear from the description which is rendered below with reference tothe accompanying drawmg.

Referring now to the drawing, numeral 1 indicates a tubular metalliccathode carrier upon which is provided the intermediate layer 2 carryingthe emission layer proper indicated at 3. Directly upon the surface ofthe emission layer 3 are disposed metallic rods 4in the illustratedexample four rodst0 which is connected a very high ohmic resistor 5. Thelatter is in turn connected to a high voltage of the voltage source, forexample, the anode voltage, so as to cause a current to flow between therods 4 and the cathode carrier 1 which etiects heating of theintermediate layer 2 to an extent sufiicient to cause the emission layer3 to begin emitting, although initially slightly, at least within theregion of the firing anode. The initial heat thus produced flows moreand more to the remaining parts of the emission layer 3, for example,between two neighboring metal strips or rods of the auxiliary anode, sothat these parts will likewise begin to emit. The working electrodeproper assumes thereby and also due to the increasing voltage drop atthe high ohmic resistor in the auxiliary discharge path, the emittingelectron current which is required for the further heating of theintermediate layer, while the firing voltage lying at the firing anodedrops increasingly at the high ohmic resister 5 and exerts no furtherinfluence or rather to say no essential influence respectively upon thefurther emission or discharge.

The potential of the emitting surface with respect to the metalliccathode carrier and also with respect to a control grid that may beprovided, is due to the peculiarity of the heating of the layer veryuncertainly defined and may strongly fluctuate from cathode to cathode.Moreover, it must never happen in an amplifier tube with such a cathodethat the emission current drops for a prolonged time to zero, forexample due to disconnection at a control grid, because the temperatureof the cathode would therewith automatically drop and emission wouldstop. A simple, otherwise customary intensity control by means of acontrol grid cannot be applied to a tube equipped with such a cathode.The invention accordingly proposes to use in connection with the tubeillustrated in the drawing a deflection control for obtaining thedistribution control relative to the illustrated remaining electrodes.

The electron beam 5 emanating in operation from the cathode at thesurface of the layer 3, which is accelerated in the direction of a firstanode '7, is by means of a control electrode 8, which is with respect tothe cathode at a negative potential, bundled in such a manner that itenters more or less completely into the aperture of a second anode 9through which it reaches the collector ltl. As may be readilyappreciated, the ratio of the current amounts respectively impacting thesecond anode 9 and the collector ll can be changed, with the totalemission current remaining constant, as is aboslutely necessary formaintaining the emission with the particularly constructed cathodeemployed. It may be advantageous under certain conditions to arrange andconstruct the metallic rods operating as auxiliary anode for the firingso that they can be employed for cooperation in the distributioncontrol.

The principle of the thermionic cathode without heater is not inherentlylimited to the example described herein and illustrated in the drawing.

Changes may be made within the scope and spirit of the appended claimswhich define what is believed to be new and desired to have protected byLetters Patent.

I claim:

1. A high vacuum amplifier tube having a thermionic cathode, saidcathode comprising a conductive cathode carrier, a layer of emissionmaterial disposed thereon, and an artifically produced resistance layerdisposed between the carrier and the emission layer, said intermediatelayer having a resistance which is sufiiciently high that the constantemission current, operating as a transverse current through saidresistance layer, is operative as the sole heating means for maintainingthe cathode at operating temperature, and at least one auxiliaryelectrode disposed in engagement with said emission layer, saidauxiliary electrode being operative, when positively V biased, to forman auxiliary current path between it and said carrier for the traversingof an initial current operative to initiate emission.

2. A high vacuum amplifier tube according to claim 1, wherein saidauxiliary electrode comprises a plurality of rodlike metallic membersdisposed upon said cathode and uniformly distributed over the surfacethereof, and cir- 4s cuit means including a high ohmic resistor forconnecting said rodlike members with a positive voltage.

3. A high vacuum amplifier tube according to claim 2, wherein saidintermediate resistance layer is made of oxides of earth alkali metalsand/ or earth metals.

4. A high vacuum amplifier tube according to claim 2, wherein saidintermediate resistance layer is made of substances selected from theclass consisting of aluminum oxide magnesium oxide and calcium oxide.

5. A. high vacuum amplifier tube according to claim 2, wherein saidintermediate resistance layer consists of high resistance substancesforming intermediate layers in customary oxide cathodes.

6. A high vacuum amplifier tube according to claim 2, comprising currentdistributing control means operating in accordance with the deflectionprinciple.

7. A high vacuum amplifier tube according to claim' 6, wherein saidcurrent distributing means comprises a control electrode and at leasttwo subdivided auxiliary anodes.

8. A high vacuum amplifier tube according to claim 6, whereinsaidcurrent distributing means comprises a control electrode and at leasttwo slotted auxiliary anodes.

9. A high vacuum amplifier tube according to claim 6, wherein saidauxiliary electrode comprises a part of said current distributingcontrol means.

References Cited in the file of this patent UNITED STATES PATENTS

1. A HIGH VACUUM AMPLIFIER TUBE HAVING A THERMIONIC CATHODE, SAIDCATHODE COMPRISING A CONDUCTIVE CATHODE CARRIER, A LAYER OF EMISSIONMATERIAL DISPOSED THEREON, AND AN ARTIFICALLY PRODUCED RESISTANCE LAYERDISPOSED BETWEEN THE CARRIER AND THE EMISSION LAYER, SAID INTERMEDIATELAYER HAVING A RESISTANCE WHICH IS SUFFICIENTLY HIGH THAT THE CONSTANTEMISSION CURRENT, OPERATING AS A TRANSVERSE CURRENT THROUGH SAIDRESISTANCE LAYER, IS OPERATIVE AS THE SOLE HEATING MEANS FOR MAINTAININGTHE CATHODE AT OPERATING TEMPERATURE, AND AT LEAST ONE AUXILIARYELECTRODE DISPOSED IN ENGAGEMENT WITH SAID EMISSION LAYER, SAIDAUXILIARY ELECTRODE BEING OPERATIVE, WHEN POSITIVELY BIASED, TO FORM ANAUXILIARY CURRENT PATH BETWEEN IT AND SAID CARRIER FOR THE TRAVERSING OFAN INITIAL CURRENT OPERATIVE TO INITIATE EMISSION.